This invention relates to transferring encrypted packets over a public network.
Referring to FIG. 1, while executing a variety of software applications, 10, 12, 14, for example, Telnet 10 or Microsoft.TM., Inc. Word.TM. 12, computers 16 and 18 may exchange data over networks 20, 21, for example, a telephone company network, a private network, or a public network such as the internet or X.25. The applications communicate using network protocols 22, 24, 26, for example, transmission control protocol/internet protocol (TCP/IP) 22 or internet packet exchange (IPX) 24, through application programming interfaces 28, 30, 32. Through application programming interfaces 34, 36, 38, the network protocols communicate with network drivers 40, 42, 44 to direct network interface hardware 46, 48 to transfer data over the networks.
While on a network, data being transmitted, including the addresses of the source and destination computers 16, 18, is accessible to others who may be monitoring the network. For security, the data is often encrypted before being sent on the network.
Referring also to FIG. 2, for additional security, firewall computers 16, 18, which have direct access to a network 20 may be used to prevent unauthorized access to internal/private networks 50, 52. For example, when an internal network driver 53 within firewall computer 16 receives data from an internal computer 54 that is destined for a computer 56 on a public network, it encrypts the data and the addresses of source computer 54 and destination computer 56. Computer 16 then prepends to the encrypted data a new IP header including its own address as well as the address of a destination computer, which may also be a firewall computer, e.g., computer 18.
When a firewall computer receives a network packet from the network, it determines whether the transmission is authorized. If so, the computer examines the header within the packet to determine what encryption algorithm was used to encrypt the packet. Using this algorithm and a secret key, the computer decrypts the data and addresses of the source and destination computers 54, 56 and sends the data to the destination computer. If both the source and destination computers are firewall computers, the only addresses visible (i.e., unencrypted) on the network are those of the firewall computers. The addresses of computers on the internal networks, and, hence, the internal network topology, are hidden. This has been termed "virtual private networking" (VPN).
Encrypting/decrypting data has been performed by complex security software within applications or, to simplify the applications, encrypting/decrypting has been performed within the protocol stack of network protocols.